With recent higher-image-quality, higher-speed ink-jet printing apparatuses, many printing apparatuses employ a DC motor as a driving source, and adopt servo control capable of feeding back position detection information of an encoder to perform high-precision position control and high-speed driving.
Control using a DC motor can realize driving by high-speed rotation without any step-out, unlike control using a pulse motor.
Position information of the motor can be detected at high precision by using an encoder signal. The detected information is fed back to a motor control rule to control the velocity, and thus positioning to a target position can be performed at high precision.
The printing velocity of a printing apparatus has conventionally been controlled on the basis of several settings determined in advance. For example, as for the printing velocity, printing modes such as a high-quality mode which realizes a normal printing quality, a high-speed mode which realizes high-speed printing, and a super-high-quality mode which realizes the highest quality are provided. Settings with different carriage driving velocities and different convey velocities for conveying a printing medium are determined in advance for the respective printing modes.
The driving velocity of the motor in each mode is determined from many factors such as the relationship between the motor torque and the load of the mechanical system, noise generated upon driving, sheet feed performance, and ink discharge frequency. Particularly in a mode which realizes high-speed printing, the driving velocity is determined on the basis of the relationship (torque margin) between the motor torque and the load of the mechanical system. Control for driving the motor is executed with a predetermined margin so as to prevent driving of the motor from becoming an overload to the rated torque.
In order to ensure a torque margin, a motor operation profile (control command) is so determined as to assure operation under the worst imaginable load condition (maximum load). The DC motor is servo-controlled on the basis of the determined operation velocity and acceleration/deceleration pattern.
A conventional printing apparatus assumes a use form in the worst environment or state, and sets the operation profile of each mode with a margin for the performance of the DC motor so as to keep a predetermined printing quality and printing velocity in order to assure predetermined operation even in the worst state. Printing apparatuses are spread worldwide, and various temperature environments and use frequencies are assumed. Depending on the operation pattern, an unnecessarily large margin may be ensured (over-specification).